Manufacture of integrally finned tubing

ABSTRACT

Apparatus for finning tubes comprising three arbors provided with a multiplicity of finning discs and skewed relative to a reference line representing the path of travel of a tube so that a continuous integral helical fin is produced on a length of tubing. The discs are separated into three groups, the groups being separated axially by cylindrical spacers. The first group comprises discs of progressively increasing diameter. The second group comprises discs of equal diameters; the size thereof being equal to the size of the diameter of the last disc of the first group and the size of the diameter of the first disc of the last group. The last group of discs on each arbor comprises discs of progressively increasing diameter for the first part of the group and of equal diameter for the last part of the group.

United States Patent Inventors Carl J. Sch-eh;

Llverpool; Frank P. Wllers, Syracuse, both of, N.(. Appl. No. 804,561 Filed Mar. 5, I969 Patented Aug. 14, 197 l Assignee Carrier Corporation Syracuse, NY.

MANUFACTURE OF INTEGRALLY FINNED TUBING 2,983,168 S/l96l Laban .r 72/l00 3,383,893 S/l968 C0unts.....,... 72/98 FOREIGN PATENTS 89l,580 l2/l943 France. 72/98 Primary Examiner-Richard J. Herbst Attorney.r Harry 0. Martin, Jr. and J Raymond Curtin ABSTRACT: Apparatus for finning tubes comprising three ar bors provided with a multiplicity of finning discs and skewed relative to a reference line representing the path of travel of a tube so that a continuous integral helical fin is produced on a length of tubing. The discs are separated into three groups, the groups being separated axially by cylindrical spacers The first group comprises discs of progressively increasing diameter The second group comprises discs of equal diameters, the size thereof being equal to the size of the diameter of the last disc of the first group and the size of the diameter of the first disc of the last group. The last group of discs on each arbor comprises discs of progressively increasing diameter for the first part of the group and of equal diameter for the last part of the group,

PATENTED AUG24 IHYI FIG. 3

26 FIG. 4

mm M FRANK F.

nu 3 F 3 3 ATTORNEY.

MANUFACTURE OF INTEGRALLY FINNED TUBING BACKGROUND OF THE INVENTION This invention relates to the manufacture of integrally finned tubing of the kind used in heat transfer apparatus, and more particularly it relates to the tooling for producing singlelead fins on high performance tubing and a method of forming a continuous fin integrally about a length of tubing.

Integral helical external fins are formed on lengths of tubing by subjecting the tubing to a circumferential rolling pressure radially inward against axially spaced peripheral portions of a tube to extrude material from the wall of the tubing radially outward to form fins. The apparatus for forming fins on tubing generally includes a plurality of forming roll assemblies which precision spaced about the tube and are mounted to move toward the tube. Each forming roll assembly has die means mounted on a supporting arbor; the die means define axially spaced peripheral portions with grooves therebetween. The die means are commonly discs which are graduated in diameter and width to progressively form fins of the desired size and height.

Preferably, three forming roll assemblies are mounted with their axes essentially parallel to each other but spaced l20 apart. The axes of the roll assemblies are at a slight skew angle in the customary manner so as the tube is advanced through the apparatus, the fins will be formed about the surface to define a helical configuration. Radial movement of the roll assemblies is controlled by sleeve-shaped cams; each of the arbors being mounted in an associated cam. The sleeve-shaped cams are joumaled within mating bores disposed on the inner surface of a substantially cylindrical member, the outer surface thereof defining the outer periphery of the tube finning head assembly, the member forming a housing for the other components of the assembly. The mating bores establish the desirable skew angle for the axes of the roll assemblies. lt has been determined that the heat transfer performance of finned tubing is effected by several factors. The fin pitch is one of these factors. Generally, increasing the number of fins per inch so that a fine pitch" fin is obtained tends to improve the heat transfer characteristic of the tube. As used herein, the term fine pitch shall refer to finned tubing exceeding 20 fins per inch. Other factors are equally important, and they include the thickness of the tube wall and fin configuration. The wall thickness of tubing normally employed in heat transfer apparatus before any finning operation has been performed is 0.053 inch. The wall thickness is reduced to 0.035 inch by the finning process. Heat transfer performance can be improved by using thin wall, high performance tubing. The thickness of the wall of such tubing before the fins are extruded thereon is 0.047 inch. After the finning operation, the residual thickness of the wall is reduced to 0.028 inch.

As noted above, a further factor influencing the heat transfer performance of finned tubing is the configuration of the fin. The optimum fin configuration to obtain maximum heat transfer is a fin of relatively thin tip thickness.

Tool arrangements heretofore used for 0.053 inch wall tubing do not produce a satisfactory fin on the lighter 0.047 inch wall tubing when fine pitch fins with relatively this tip thickness are desired.

The disc arrangements heretofore used produced finned tubing with poor fin specification when used on high performance 0.028 inch tubing. ln addition, these arrangements also produced fins with hairs. Hairs is the term applied to fine slivers of metal which are partially separated from the finned tubing adjacent the roots of the fins.

These problems have been overcome by arranging the discs in a particular sequence in the manner hereinafter disclosed.

SUMMARY OF THE INVENTION The present invention pertains to a novel disc arrangement for rolling fin pitch, relatively thin topped fins on high performance, thin-walled tubing, otherwise known as 0.028 inch residual wall tubing.

The discs are arranged into three groups on the arbor. The first group comprises a series of three discs. These discs initially make contact with unfinned or prime surface tubing as it is directed into the finning machine. The diameter of the second disc in the first group is substantially larger than the diameter of the first disc of the group. The difference between the diameters of this pair of discs is much larger than the difference between the diameters of any other pairs of adjacent discs. The reason for the abrupt change in diameter from the first disc to the second disc is so a sudden plunge into the raw stock may be made before the stock is work hardened by a number of fin discs making contact with the stock, thereby causing brittleness.

After the first three discs, a spacer exactly four times the thickness of any disc of the first group, is inserted to separate the first group of discs from the second group. The spacer provides a stress equalizing factor by providing a pause in the working of the tube stock.

The second group of discs comprises a series of three discs of equal dimensions. These discs are of the same dimensions as the last disc of the first group and of the first disc of the last group to be later described. By maintaining the disc dimensions without any changes, several advantages are obtained. An additional stress equalizing interval is added to the finning process. Furthermore, the tube material will be set against a mandrel about which the tube stock is rotating, thereby reducing the inside diameter as is desired.

A second spacer separates the second group of discs from the last or third group. This spacer is 0.005 inch thicker than the first spacer. The additional 0.005 inch will offset the backward deflection of the first disc of the last group produced by the elongation of the tube stock during the finning process. Further stress equalization is also obtained through use of the second spacer.

The last group of discs comprises a series of seven discs. The first four discs are in a progression wherein the diameters thereof will be increasing in the direction of advance of the tube. The last three discs are of equal dimensions and will finish the fin to its desired dimensions, including the final tip thickness, tolerance, and fin weight thereof. It should be noted that the disc arrangement hereinabove described will be exactly the same on all three arbors.

The novel fin disc arrangement herein disclosed will hen ceforth enable fine pitch finned tubing to be produced whereby the optimum configuration for the maximum heat transfer may be extruded onto high performance, thin-walled tubing. It is now possible to roll single-lead, fine pitch fins on high performance 0.028 inch residual wall tubing without encountering the problems hereinbefore mentioned.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic elevational view of an arbor containing fin forming discs and of a tube being finned;

FIG. 2 is a fragmentary elevational view on an enlarged scale showing the cross-sectional shape of the peripheral portion of a representative finning disc;

FIG. 3 is a diagrammatic view illustrating the relationship between a tube being finned and the three finning rolls;

FIG. 4 is a fragmentary sectional view on an enlarged scale showing the profile of a typical finned tube presently known to the art; and

FIG. 5 is a fragmentary sectional view on an enlarged scale of a typical finned tube produced by the fin disc arrangement herein disclosed.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is illustrated a preferred embodiment of the invention disclosed herein wherein like numerals refer to like parts.

Referring particularly to FIG. 1, there is illustrated an arbor [0 having three groups of discs ll, 12, and 13 mounted thereon. The first group of discs 11 is separated from the second group of discs 12 by a first spacer 14. The second group of discs 12 is separated from the third group of discs 13 by a second spacer 15. As shown, the assembly of discs and spacers is axially positioned against a radially extending flange 16 on the arbor 10 by suitable means such as, for example, a lock nut 17 or the like. The discs and spacers are secured to the arbor by a key, not shown, so the discs and spacers cannot rotate relative to the arbor.

In practice, three arbors are employed spaced at approximately l20 intervals around the path of advance of a tube, a portion of the tube being indicated by the numeral 20in FIG. I.

The arbors are held in a finning head assembly (not shown) which is mounted on the finning machine (also not shown). The three arbors are rotated, thus imparting a rotating movement to the tube positioned therebetween. As is best shown by FIG. 1 of the drawings, the axes 22 of the arbors 10 are at a slight skew angle relative to the axis 23 of the tube 20. Due to the angular relationship between the axes 22 of the arbors l and the axis 23 of the tube 20, the rotation of the arbors causes the tube 20 to advance as it rotates, thus forming helical grooves thereon and ultimately shaping the metal between adjacent convolutions into the form of heat transfer fins 21 as is desired.

Referring now to FIG. 3, the relationship between a tube being finned and the three arbors spaced therearound can best be seen. The tube 20 is shown in simultaneous contact with discs on three arbors identified respectively as 10, a, and [0 b. In the figure, the direction of rotation of the tube and arbors is as illustrated, and it will therefore be observed that any particular point on the tube moves in sequence, both radially and axially, from discs carried by the arbor 10b. It should be specifically noted that the arrangement of discs on each of the three arbors will be the same.

It has been determined that fine pitch fins improve the heat transfer characteristic of finned tubing. Additionally, heat transfer performance can be improved by using thin wall, high performance tubing, Such tubing is generally known in the art as 0.028 inch residual wall tubing. The fin disc arrangement hereinafter more fully disclosed will enable those skilled in the art to manufacture single-lead, fine pitch, relatively thin tipped finned tubing on high performance, thin wall tubing.

Again referring to FIG. I, the first group of discs 11 comprises a series of three discs represented by the numerals l, 2, and 3 respectively.

The three discs I, 2, and 3 are primarily for the purpose of beginning fin formation and producing the major metal movement as the root diameter is initially formed and subsequently refined. Once the primary fin is formed, the succeeding discs operate principally to control the profile of the fins and the changes produced by the discs in the latter groups 12 and 13 are accordingly of smaller magnitude.

The diameter of disc 2 is relatively larger than the diameter of disc I. The difference therebetween is greater than the difference in diameters between any other consecutive discs of the three groups ll, 12, and 13. Discs 1 and 2 are the first to make contact with the raw tube stock. For the purpose of understanding the movement of metal in response to the action of the discs, disc 1 forms an initial scoring of the mandrel supported tube. The reason for the abrupt increase in diameter size from disc I to disc 2 is so a sudden plunge can be made into the tube stock before the metal is work hardened by a number of fin discs making contact, thereby causing brittleness. Thus, the scoring provided by disc 1 serves as a track for accommodating disc 2 which enlarges the scoring as described. The third disc 3 of the first group is slightly larger in diameter than disc 2 and thereby further increases the depth of the groove.

Separating the first group ll from the second group 12 is a substantially cylindrical spacer l4. Spacer 14 is exactly four times the thickness of any disc of the first group ll. The spacer provides a stress equalizing factor by providing a pause in the working of the tube stock 20.

The second group of discs l2 comprises a series of three discs. Reference numeral 3 is used to designate these discs, thereby indicating that the three discs of the second group 12 are exactly the same as the last disc of the first group II. By maintaining the disc dimensions without any changes, several advantages are obtained, An additional stress equalizing interval is added to the finning process. Furthermore, the tube material will be set against a mandrel (not shown) about which the stock is rotating, thereby further establishing the root diameter 24 of the fins. By maintaining the discs 12 at the same depth as the last disc of the first group 11, the inherent tendency of the tube metal to return to its original position will be overcome.

Separating the second group of discs 12 from the third group of discs 13 is a second substantially cylindrical spacer 15. The spacer I5 is 0.005 inch longer than the first spacer 14. The additional 0.005 inch will offset the backward deflection of the first disc of the last group produced by the elongation of the tube stock during the finning process. Additional stress equalization is obtained through the utilization of the second spacer IS.

The last group of discs l3 comprise a series of seven discs. The first four discs 3, 4, 5, and 6 respectively are in a progression wherein the diameters thereof will be increasing in the direction of advance of the tube, such advance being represented by the solid arrow of FIG. I. The four discs 3, 4, 5, and 6 will establish the final root diameter 24 and will further shape the fin 21. The last three discs 7 are of equal dimensions and will finish the fin to its desired dimensions, including the final tip thickness, tolerance, and fin weight thereof.

Referring now to FIG. 2, there is diagrammatically shown an enlarged elevational view of the periphery of a typical disc 25. The diameter of the discs is represented by D and the angle of inclination of the sides of the discs is represented by F.

Generally, the discs are of a generally increasing diameter D, with disc No. 1 being the smallest and discs No. 7 the largest. As noted previously, the increase in diameter D between the first discs to contact the tube 20, Nos. 1 and 2, is greater than the increase in diameter between any consecutive discs thereafter following.

Not only are the consecutive discs of generally increasing diameter, but their shapes are also modified to produce the fin configuration desired, as it is formed outwardly by the displacement of metal. The sides of the discs to first contact the tube are inclined at a substantial angle F, thereby producing a relatively narrow disc at its extreme periphery. This in turn will make the initial grooves formed by the discs relatively nar row and the tips of the first fin formation will be relatively thick. The finishing discs 7 are relatively wider at the extreme periphery and therefore the sides are tapered at a lesser angle F. This in turn will cause the grooves between adjacent fins to be relatively wide, and the final fin will be relatively thin at its tip as is desired.

Now referring to FIGS. 4 and 5, there is shown for comparison fins formed prior to the novel disc arrangement herein disclosed and fins that may be produced hereafter, wherein FIG. 4 represents the old" fins and FIG. 5 represents the novel fin.

The novel fin disc arrangement hereinbefore disclosed may be utilized to produce a relatively thin top fin, heretofore unknown to the art. As previously noted, a tip thickness of relative thinness is a desirable feature, since such a fin characteristic will increase the heat transfer capabilities of the finned tubing.

Referring particularly to FIG. 4, a tube 26 has extruded thereon fins 27. The thickness of the tips 28 of fins 27 is relatively large whence compared to the thickness of the tips 3] of the fins 21 extruded on the tube 20 shown in FIG. 5.

While we have described and illustrated a preferred embodiment of our invention, it will be understood that our invention is not limited thereto, since it may be otherwise embodied with the scope of the following claims.

We claim:

diameter of the first disc of said first group.

5. Apparatus according to claim I wherein the residual wall 1. Apparatus for forming single-lead fine pitch helical fin formations on tubing which comprises:

a. three arbors positioned with their axes spaced laterally from and substantially equally spaced around the axis of said tubing after the firming process has been completed is 0.028 inch.

which a tube advances during a P g i firming 5 6. A method of forming a length of tubing with an integral operation and disposed at a small angle thereto; h h ll extending fin i i a P f y 0f d disfis said for a. subjecting a length of tubing to an initial circumferential rotat on therewith, said i belng of mcreas' rolling pressure applied in a radially inward direction on "8 dlamem' m the f f of the advance of the axially spaced, helically aligned peripheral portions of inof generally mueasmfl p p f cross 9 radlus of creasing radial extent whereby material is displaced from Y of dacfeasmg angulaf'ty beiween the wall of said tubing radially outward and the maximum pmlheml 0f the f of the 'g P root diameter for said fin is substantially reached;

' a first,spacer on each of sad Pmvdmg fi b. relieving said length of tubing from said rolling pressure sepamuon between first and a i s of f for a predetermined interval, thereby relieving stresses spacer on each of said arbors providing axial separation formed during the initial step; f 'f a second and 3 9 of 4 bots c. subjecting said length of tubing to a rolling pressure of "9'" angle substantially the same magnitude, said helically aligned axis of advance of the tube such that a contlnuous helical peripheral portions operating to define m ore accurately fin is produced, the discs of the first group to engage a said root diamemr of said Ti offan g fif r zg z fi' Increase; d. again relieving said length of tubing from said rolling mg m mm m: t e o t secon pressure for a predetermined interval, thereby further regroup all belng ofthe same diameter as the last disc of the Having any stresses formed and gt g g g zzs rigg 53 22: z g gs z z? :2: e. again subjecting said length of tubing to a rolling press ivel increasin diameter from d isc to disc for :l'le first 25 sure said rolling Pressure initially being applied in a ram.

oniyon of said and ofe ml diameter from disc to ally inward direction displacing material from said wall of g for the last g g ofsaid group said tubing radially outward, thereby establishing the final 2. Apparatus as defined in claim 1 in which said first pacer i i j i i theream." r zi is exactly four times the thickness of a disc in said first group. P 311 ha! lrectlon,h t are y squeezing br 1 ms 3. Apparatus as defined in claim 2 in which said second formed t e pnor e In ""P here y f spacer is 0.005 inch thicker than said first spacer. f radlany F' f fin thereby bemg 4. Apparatus as defined in claim 1 wherein the diameter of d'mensloned to final helght and thmkness' the second disc of said first group is relatively larger than the UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 9 Dated August E I, 1971 lnventofls) CARL J. SCHMELING 8c FRANK F. WALTERS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 60, "this" should read --thin- Column 1, line 73, "topped" should read -tipped-- Column 3, line 32, between "carried" and "by" insert --on arbor 10 to discs carried by the arbor 10a and the discs carried-- Column 4, line 63, "top" should read --tip- Signed and sealed this 23rd day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GO'ITSCHALK Attesting Officer Commissioner of Patents 

1. Apparatus for forming single-lead fine pitch helical fin formations on tubing which comprises: a. three arbors positioned with their axes spaced laterally from and substantially equally spaced around the axis along which a tube advances during a progressive finning operation and disposed at a small angle thereto; b. a plurality of finning discs mounted on said arbors for rotation therewith, said discs being of generally increasing diameter in the direction of the advance of the tube, of generally increasing peripheral cross section radius of curvature and of decreasing angularity between peripheral portions of the sidewalls of the discs; and c. a first spacer on each of said arbors providing axial separation between a first and a second group of discs, spacer on each of said arbors providing axial separation between a second and a third group of discs, said arbors being disposed at the angle at which their axes cross the axis of advance of the tube such that a continuous helical fin is produced, the discs of the first group to engage a given portion of an advancing tube progressively increasing in diameter from disc to disc, the discs of the second group all being of the same diameter as the last disc of the first group and the first disc of the last group, and the last group of discs on each arbor comprising discs of progressively increasing diameter from disc to disc for the first portion of said group and of equal diameter from disc to disc for the last portion of said group.
 2. Apparatus as defined in claim 1 in which said first spacer is exactly four times the thickness of a disc in said first group.
 3. Apparatus as defined in claim 2 in which said second spacer is 0.005 inch thicker than said first spacer.
 4. Apparatus as defined in claim 1 wherein the diameter of the second disc of said first group is relatively larger than the diameter of the first disc of said first group.
 5. Apparatus according to claim 1 wherEin the residual wall of said tubing after the finning process has been completed is 0.028 inch.
 6. A method of forming a length of tubing with an integral helically extending fin comprising: a. subjecting a length of tubing to an initial circumferential rolling pressure applied in a radially inward direction on axially spaced, helically aligned peripheral portions of increasing radial extent whereby material is displaced from the wall of said tubing radially outward and the maximum root diameter for said fin is substantially reached; b. relieving said length of tubing from said rolling pressure for a predetermined interval, thereby relieving stresses formed during the initial step; c. subjecting said length of tubing to a rolling pressure of substantially the same magnitude, said helically aligned peripheral portions operating to define more accurately said root diameter of said fin; d. again relieving said length of tubing from said rolling pressure for a predetermined interval, thereby further relieving any stresses formed; and e. again subjecting said length of tubing to a rolling pressure, said rolling pressure initially being applied in a radially inward direction displacing material from said wall of said tubing radially outward, thereby establishing the final root diameter, said rolling pressure thereafter being applied in an axial direction, thereby squeezing the fins formed by the prior steps, the fin material thereby being further displaced radially outward, said fin thereby being dimensioned to its final height and thickness. 